Changes of State
How energy transfer rearranges particles without changing the substance
Big idea: A substance can change between solid, liquid, and gas when energy is transferred. During a change of state, the particles remain the same chemical particles; their spacing, motion, and attractions change. Therefore a change of state is a physical change, not the formation of a new substance.
Learning goals:
- name and distinguish melting, freezing, evaporation, boiling, condensation, sublimation, and deposition;
- explain each transition with a particle-and-energy model;
- read plateaus and sloping sections on heating and cooling curves;
- separate evaporation from boiling;
- apply the model to weather, food preservation, refrigeration, and materials while working safely.
1. One substance, three common states
A state of matter describes the large-scale behaviour of a substance. A solid keeps its own shape and volume. A liquid keeps nearly the same volume but flows to take the shape of its container. A gas has neither a fixed shape nor a fixed volume and spreads to fill the available space. These observations are explained with a particle model: particles in a solid are closely packed in an ordered arrangement and vibrate; particles in a liquid remain close but move past one another; particles in a gas are much farther apart and move freely in many directions.